1. Field of the Invention
The present invention relates to a high-temperature gas turbine, a compressor for the high-temperature gas turbine, a rotor shaft for the compressor and a heat-resistant steel for the rotor shaft.
2. Description of Related Art
In a compressor rotor for a conventional large-size high-temperature gas turbine, disks (seventeen stages) are fixed thereon by bolts, as disclosed in, for example, Publications of Japanese Laid-Open Patent Applications shou 63-171856 and hei 2-101143. The disks from a first stage to a twelfth stage at a rotor air inlet (low temperature) side are made of a 3% Ni--Cr--Mo--V low alloy steel, while the disks from a thirteenth stage to a sixteenth stage at a rotor air outlet (high temperature) side are made of a Cr--Mo--V low alloy steel having a high strength at high-temperature. The disk of a last stage is made of martensitic steel. This divided rotor type compressor suffers from problems that manufacture thereof requires too many hours and a rupture readily occurs.
Mitsubishi Juko Technical Report, Vol. 27, No. 1 (1990-1) describes another gas turbine compressor with a monolithic rotor shaft.
The disk type gas turbine rotors disclosed in Publications of Japanese Laid-Open Patent Applications shou-63-171856 and hei-2-101143 have disadvantages that manufacture thereof requires too many hours, the bolts are loosened due to creep thereof when a temperature of the compressor is high and thus must be re-tightened with troublesome work to avoid vibrations, and replacement of a broken blade is troublesome.
In recent years, there is a tendency for a capacity of gas turbines to increase and thus for the temperature to also increase.
The compressor rotor for a large-size high-temperature gas turbine is rotated at a high speed in a wide temperature range between room temperature and 500.degree. C. Hence, the monolithic rotor must be made of a material whose room temperature tensile strength is .gtoreq.85 kg/mm.sup.2, fracture appearance transition temperature is .ltoreq.20.degree. C. and 475.degree. C., 10.sup.5 h creep rupture strength under 475.degree. C. and 10.sup.5 hours is .gtoreq.30 kg/mm.sup.2. The aforementioned Mitsubishi Juko Technical Report does not describe a rotor material, and the compressor disclosed therein is operated at a low temperature. As a rotor material used at high temperature, above-described Ni--Cr--Mo--V steel has a high toughness at a low temperature but a low strength at high temperature, whereas the above-described Cr--Mo--V steel has a high strength at high temperature and a low toughness at low temperature.